Medical imaging diagnostic equipment generally includes a medical image capturing apparatus for capturing medical images of the interior of the body of a subject, and a medical image processing apparatus for processing the medical images. Examples of the medical image capturing apparatus include an X-ray CT apparatus (an X-ray computed tomography apparatus), and MRI (a magnetic resonance imaging diagnostic apparatus). Such a medical image capturing apparatus acquires volume data as information on the interior of the body of the subject by capturing images.
The medical image processing apparatus may use volume rendering, for example, as a visualization technology for visualization of the volume data. The volume rendering generates three-dimensional images from the volume data for example by a ray casting method of rendering an object by tracing light rays leading from an observer's eye to pixels (i.e. 3-D rendering). Further, the three-dimensional images may be sequenced in time series to form a three-dimensional time-varying image (i.e. 4-D rendering).
Here, observation of an aortic valve on a three-dimensional time-varying image, as seen from the direction of an aortic root, is most suitable for image diagnosis for the purpose of making a treatment plan for aortic stenosis, for example, deciding on valvuloplasty, valve replacement, or the like. Specifically, while the valve is moving, observations of changes in a valve orifice area are made taking into account the influence of a calcified part around the valve.
Because of a fast movement of the valve in itself, however, time-varying image reproduction which provides a simple sequential display of medical images (for example, CT images) captured in time series is deficient in the number of frames and hence is inadequate for observation of the movement of the valve. Attention is therefore being given to 4-D rendering with high time resolution which reproduces a smooth movement of the valve by generating finer time-series volume data from time-series volume data by interpolation processing.
In the above-described 4-D rendering with high time resolution, however, the smooth movement of the valve is reproduced by the interpolation processing based on nonlinear alignment, while on the other hand, the calcified part deposited on the valve becomes distorted from the nonlinear alignment. This makes it impossible to accurately diagnose the influence of the calcified part upon the changes in the valve orifice area.
A constituent of the calcified part is inherently calcium which is the same as that of a bone, and thus the calcified part undergoes no distortion by the movement of the valve, and therefore, after the interpolation processing, the calcified part does not assume its precise shape. This makes it impossible for a diagnostician to accurately diagnose influences upon the calcified part, or equivalently, a non-distorted feature part and its surroundings.